Permanent magnet (PM) generators are typically characterized by the following advantages: simple construction, high efficiency, high power factor and high power density. These types of generators are therefore well suited for direct-drive wind turbine applications (see for example EP 2 028 744).
There are several types of rotor topologies for PM synchronous generators. The configurations of the rotors can be divided into radial and transversal forms depending on the orientation of the magnetization direction of the permanent magnets. The transversal configuration is more suitable for applications requiring high power density and performance. The transversal-oriented magnet configuration is characterized by a partially non-magnetic rotor core with alternating transversal-oriented permanent magnets and pole pieces to concentrate the flux and direct it radially toward the stator teeth. The stator may be the same as in a conventional radial oriented magnet generator design (see U.S. Pat. No. 6,879,075).
As the output power of wind turbines has rapidly increased, the development of advanced generators has inherently involved the design and construction of large diameter and low speed machines. Over the past several years, high efficiency and lightweight generators using advanced magnetic materials have been developed. However, there is still a need for improvement of the generators to cope with the increasing power and efficiency requirements.